使用栈的表达式计算程序.arith_expr.c

最新推荐文章于 2024-02-08 21:48:10 发布

ljd_1881

最新推荐文章于 2024-02-08 21:48:10 发布

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CC 4.0 BY-SA版权

文章标签： struct float c null character integer

本文链接：https://blog.youkuaiyun.com/ljd_1881/article/details/1383302

本文介绍了一个简单的算术表达式解析器实现，该解析器能够处理包含整数和浮点数的四则运算，并使用栈来管理和计算表达式。文章详细展示了如何通过扫描输入字符串并应用操作符优先级规则来构建和评估逆波兰表示法。

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#include<stdio.h>

#include "arith_expr.h"

#include<assert.h>
#include<ctype.h>
#include<stdlib.h>
#ifndef True
#define True 1
#define False 0
#endif
#define NS_LEN 100
#define OS_LEN 100

struct ns
{
    struct NUM nums[NS_LEN];
    int top;
};

struct os
{
    char ops[OS_LEN];
    int top ;
};

struct os opstack;
struct ns numstack;

FILE * listing;
char * str ;
int pos;

void setNum(struct NUM * pn1,struct NUM * pn2)
{
    pn1->type = pn2->type;
    if (pn1->type == 0)
        pn1->value.ivalue = pn2->value.ivalue;
    else if (pn1->type == 1)
        pn1->value.fvalue = pn2->value.fvalue;
};

int nspush(struct NUM *num)
{
    int rel = False;
    (numstack.top)++;

    if (numstack.top == NS_LEN)
        fprintf(listing,"push error:the number stack is full/n");
    else
    {
        (numstack.nums[numstack.top]).type = num->type;
        (numstack.nums[numstack.top]).value = num->value;   //
        rel =True;
    }
    return(rel);
};

int nspop(struct NUM *num)
{
    int rel = False;
    if (numstack.top <0)
        fprintf(listing,"error:the number stack is empty to pop/n");
    else
    {
        num->type = numstack.nums[numstack.top].type;
        num->value = numstack.nums[numstack.top].value;
        rel = True;
    }

    return(rel);
};

char getNextChar()
{
    return(str[pos++]);
};

void ungetNextChar()
{ pos--;
};

void getNum(char c)
{
    char strvalue[50];
    int i,pointnum=0;
    struct NUM num;

    i = 0;
    while (isdigit(c)&&i<=49)
    {
        strvalue[i++] = c;
        c = getNextChar();
    }
    if (c=='.'&&pointnum==0)
    {
        pointnum++;
        strvalue[i++] = c;
        c = getNextChar();
        if (!isdigit(c))
        {
            fprintf(listing,"error.this num has a point .it may be a float,but after the point there is no digit/n ");
            return;
        }
        while(isdigit(c))
        {

            strvalue[i++] = c;
            c = getNextChar();
        }
    }
    else if (c=='.'&&pointnum==1)
    {
        fprintf(listing,"error:tow points/n");
        return;
    }
    ungetNextChar();
    strvalue[i] = '/0';


    if (pointnum==0)
    {
        num.type = 0; // integer
        num.value.ivalue = strtol(strvalue,(char **)NULL,10);
    }
    else
    {
        num.type = 1; // float
        num.value.fvalue = strtof(strvalue,(char**)NULL);

    }

    nspush(&num);
};

int ospush(char op)
{
    opstack.top++;
    if (opstack.top == OS_LEN)
    {
        fprintf(listing,"sorry,the operation statc is full,can not push/n");
        return(False);
    }
    opstack.ops[opstack.top] = op;
    return(1);
};
int ospop(char *op)
{
    if (opstack.top<0)
    {
        fprintf(listing,"The operation stack is empty.can not pop/n");
        return(False);
    }
    *op = opstack.ops[opstack.top--];
    return(1);
};

void displayns()   // to debug
{
    int i = 0 ;
    while (i <=numstack.top)
    {
        if (numstack.nums[i].type == 1)
            fprintf(listing,"%4.2f/n",numstack.nums[i].value.fvalue);
        else

            fprintf(listing,"%4d/n",numstack.nums[i].value.ivalue);
        i++;
    }
};
void displayos() // to debug
{
    int i=0;
           while(i<=opstack.top)
    {
        printf("%c top = %-3d/n",opstack.ops[i],opstack.top);
        i++;
    }
};

int getPriority(char c)
{
    if (c =='+'||c=='-')
        return(0);
    else if (c=='*'||c=='/')
        return(1);
    else if (c=='('||c==')')
        return(2);
    else
        return(-1);
};

int IsHigh(char src,char des)
{
    int s_prio,d_prio;

    s_prio = getPriority(src);
    d_prio = getPriority(des);

    if (s_prio < d_prio)
        return(-1);
    else if (s_prio == d_prio)
        return(0);
    else
        return(1);
};
void operate_int(int x1,int x2,char c)
{
    switch (c)
    {
        case '+':
            numstack.nums[numstack.top].value.ivalue = x1+x2;
            return;
        case '-':
            numstack.nums[numstack.top].value.ivalue = x1-x2;
            return;
        case '*':
            numstack.nums[numstack.top].value.ivalue = x1*x2;
            return;
        case '/':
            numstack.nums[numstack.top].value.ivalue = x1/x2;
            return;
    }

};

void operate_float(float y1,float y2,char c)
{
    switch(c)
    {
        case '+':
            numstack.nums[numstack.top].value.fvalue = y1+y2;
            return;
        case '-':
            numstack.nums[numstack.top].value.fvalue = y1-y2;
            return;
        case '*':
            numstack.nums[numstack.top].value.fvalue = y1*y2;
            return;
        case '/':
            numstack.nums[numstack.top].value.fvalue = y1/y2 ;
            return;
    }
};

void operate()   // pop tow from number stack
{
    int x1,x2;
    float y1,y2;
    char c;

    ospop(&c);
    if (numstack.nums[numstack.top].type==0 && numstack.nums[numstack.top-1].type==0) //integers
    {
        x2 = numstack.nums[numstack.top--].value.ivalue;
        x1 = numstack.nums[numstack.top].value.ivalue;
        operate_int(x1,x2,c);
    }
    else
    {
        if (numstack.nums[numstack.top].type==0)
            y2 = (float)(numstack.nums[numstack.top--].value.ivalue);
        else
            y2 =numstack.nums[numstack.top--].value.fvalue;
        if (numstack.nums[numstack.top].type==0)
            y1 = (float)(numstack.nums[numstack.top].value.ivalue);
        else
            y1 = numstack.nums[numstack.top].value.fvalue;
        numstack.nums[numstack.top].type = 1;
        operate_float(y1,y2,c);
    }//is

};

void getOp(char c)
{
    int temp;
    char ch;

    if (c=='/0')
    {
        while (opstack.top>-1)
            operate();
        return;
    }


    if (c=='(')
        ospush(c);
    else if (c==')')
    {
        operate();
        ospop(&c);// pop the '('
        if (opstack.top<0) // empty stack
            return;
    }
    else
    {
        if (opstack.top<0) // empty stack
        {
            ospush(c);
            return;
        }

        temp = getPriority(opstack.ops[opstack.top]);
        if (temp == 2)
        {
            ospush(c);
            return;
        }

        temp = IsHigh(opstack.ops[opstack.top],c);

        while(temp>=0)
        {

            operate();    // has poped one item
            if (opstack.top<0) // empty stack
            {
                ospush(c);
                return;
            }
            temp = IsHigh(opstack.ops[opstack.top],c);

        }
        if (temp<0)
            ospush(c);
    }
};

void init(FILE * fp,char * expr_str)
{
    listing = fp;
    str = expr_str;
    pos = 0;
    numstack.top = -1;
    opstack.top = -1;
};

struct NUM * compute()
{
    char c;
    struct NUM * result = NULL;

    c= getNextChar();
    if (!(isdigit(c)|| c=='('||c==')'))
    {
        printf("error:the first character is not a digit/n");
        return(result);
    }

    while (c!='/0')
    {
        if (isdigit(c))
            getNum(c);
        else if (c=='+'||c=='-'||c=='*'||c=='('||c==')')
            getOp(c);
        c = getNextChar();
    }
    getOp(c);

    result = (struct NUM * )malloc(sizeof(struct NUM ));
    assert(result != NULL);
    setNum(result,numstack.nums+numstack.top);

    return(result);
};